1. Field of the Invention
The present invention relates to an electric charge control device for charging a secondary battery with electricity installed on a vehicle, and to a load driving device using the electric charge control device.
2. Description of the Related Art
In recent years, developments have progressed in establishing technologies to drive various loads installed in an automobile by using a high-voltage power source (42 volts) connected to a motor-generator, which is advantageous for improving mileage.
However, a high voltage cannot be applied to some low-voltage-operating loads such as an electric control unit (ECU) installed in an automobile. In order to supply electricity to these loads, a DC/DC converter is used for converting the high voltage into a low voltage of 14 volts, which is a conventional voltage standard. As a low-voltage battery to be used upon driving low-voltage loads while using the DC/DC converter, use of an environmentally friendly secondary battery is considered instead of a lead accumulator.
Nevertheless, upon using a secondary battery, the secondary battery used to be charged by a constant voltage in line with temperature characteristics thereof. However, in a case of using a secondary battery made of nickel-hydrogen or the like, it is preferred to charge the battery with a low electric current in order to improve charging efficiency.
It is an object of the present invention to provide an electric charge control device capable of charging a secondary battery with electricity in a state of high regulator efficiency, and to provide a load driving device using the electric charge control device.
The first aspect of the present invention provides an electric charge control device, comprising: an electric power source for supplying a first voltage; a converter connected to the electric power source for converting the first voltage into a second voltage which is lower than the first voltage; a secondary battery for charging a direct-current voltage from the converter; a switching regulator for inputting the second voltage from the converter and switching to vary an output voltage which is supplied to the secondary battery; a series regulator for inputting the second voltage from the converter and adjusting power consumption to vary an output voltage which is supplied to the secondary battery; a voltage detector for detecting the output voltage from the switching regulator and the series regulator; and a controller for controlling the output voltage based on a voltage value detected by the voltage detector so as to charge from any one of the switching regulator and the series regulator to the secondary battery with a constant electric current.
According to the first aspect, the output voltage value is controlled so that the secondary battery is charged with a constant electric current from the switching regulator or the series regulator based on the voltage values detected by the voltage detector. Therefore, when the output voltage of the switching regulator or the series regulator is varied in accordance with a charged voltage of the secondary battery, it is possible to use one of the regulators having a higher converting efficiency in response to the output voltage. Hence, the secondary battery can be charged with high regulator efficiency.
The second aspect of the present invention provides the electric charge control device according to the first aspect of the present invention, wherein the controller performs controlling so that the secondary battery is charged by the switching regulator when the voltage value is at a predetermined value or below, the controller performs controlling so that the secondary battery is charged by the series regulator when the voltage value is at the predetermined value or more.
According to the second aspect, the switching regulator is used when the voltage values detected by the voltage detector are at the predetermined value or below because the charged voltage of the secondary battery is low, and the series regulator is used when the voltage values is the predetermined value or more because the charged voltage is high. Since one of the regulators with a higher converting efficiency is thus selected for use based on the predetermined value, the secondary battery can be charged with high regulator efficiency.
The third aspect of the present invention provides the electric charge control device according to the second aspect of the present invention, wherein the controller retains the predetermined value indicating an output voltage at which the efficiency of the series regulator exceeds the efficiency of the switching regulator.
According to the third aspect, the controller retains the predetermined value indicating the output voltage at which the efficiency of the series regulator exceeds efficiency of the switching regulator. Therefore, it is possible to use the regulator with the greater efficiency by switching between the switching regulator and the series regulator so as to set an electric current value to enhance the efficiency of the secondary battery.
The fourth aspect of the present invention provides the electric charge control device according to the second aspect of the present invention, wherein the controller performs controlling so that the output voltage from any one of the series regulator and the switching regulator is set to a value slightly higher than a charged voltage of the secondary battery.
The fifth aspect of the present invention provides a load driving device, comprising: an electric power source for supplying a first voltage; a converter connected to the electric power source for converting the first voltage into a second voltage which is lower than the first voltage; an electric charge control unit connected to the converter; a relay provided between the converter and the electric charge control unit; a switching unit connected to the relay; a load unit connected to the converter and the relay; and a secondary battery connected to the electric charge control unit and the relay for charging a direct-current voltage from the converter, the electric charge control unit, comprising: a switching regulator for inputting the second voltage from the converter and switching to vary an output voltage which is supplied to the secondary battery; a series regulator for inputting the second voltage from the converter and adjusting power consumption to vary an output voltage which is supplied to the secondary battery; a voltage detector for detecting the output voltage from the switching regulator and the series regulator; and a controller for controlling the output voltage based on a voltage value detected by the voltage detector so as to charge from any one of the switching regulator and the series regulator to the secondary battery with a constant electric current, wherein an electric charge is supplied from the secondary battery to the load unit when the relay is set to a conductive state owing to a signal from the switching unit, and wherein the electric charge is supplied from the converter to the load unit when the relay is set to an open state.
According to the fifth aspect, the electric charge control unit is provided for controlling the output voltage value so as to charge the second battery with a constant electric current from the switching regulator or the series regulator based on the voltage values detected by the voltage detector. In this way, the second battery can be charged efficiently. Since the electric charges are supplied from the converter and from the secondary battery, it is possible to drive the load unit stably.
The sixth aspect of the present invention provides the load driving device according to the fifth aspect of the present invention, wherein the relay is set to the open state when the converter is in operation, and
the relay is set to the conductive state when the converter stops operating.
The seventh aspect of the present invention provides the load driving device according to the fifth aspect of the present invention, wherein the load unit is a load driven by a voltage lower than the first voltage.